Absorption - Introduction to Carbon Capture and Sequestration - page 209

so small that the contribution of nitrogen to the heat of desorption can be
ignored.
For the MEA solution, this energy is q tot =

8,776 kJ/kg CO 2 . If we
compare this with the minimum energy for the separation, 158 kJ/kg CO 2
(see Section 4.2), we see that our process requires 50 times more energy
than the thermodynamic minimum. A good rule of thumb is that the
chemical process industry should be operating within a factor of 2-3
times the thermodynamic minimum. If we were to operate such an
absorption process without modifi cation, very little (if any) energy would
be left for producing electricity. The fact that one can in practice design
a relatively effi cient process using MEA illustrates how clever engineering
can reduce the parasitic energy to very reasonable levels.

Section 7
Optimization of an amine
scrubber

( This section is based on a guest lecture given by Professor Gary
Rochelle, University of Texas, Austin. )
So we've covered the fact that a simple absorption process requires
enormous amounts of energy. In our calculation in the previous section
we assumed that all the heat supplied to the stripper is lost. However, by
using heat exchangers we can recover a large fraction of the heat (see
Figure 5.7.1 ). Because we also need to compress the CO 2 , integrating
this compression in the optimization is important.
In this section, we will illustrate how chemical engineering tools can
be used to optimize the absorption process [5.13]. This engineering
approach involves selecting the optimal solvent together with a careful
analysis of all steps to see how much energy each step loses compared
to the theoretical minimum. Figure 5.7.2 shows how incorporating these
steps has reduced the energy costs of carbon capture.